Land
Page 305
This was particularly the case on the western side of the Council and the
Lefevre Peninsula, which underwent major land filling, levee development, and
redirection of the original Port River and associated low lying marsh areas that
naturally occurred in the coastal areas of metropolitan Adelaide prior to
European settlement.
Over time, the land on the Lefevre Peninsula in particular has become prone to
a significant level of ‘subsidence’ caused by ongoing downward compaction of
the historic fill material, and exacerbated by the extraction of groundwater from
aquifers for over a century, causing some collapse of underground aquifers.
The most recent levelling data provides the following land subsidence statistics.
Table 69: Average Land Subsidence (1983-1994) relative to rock pin bench
marks at the Tollgate
Over a 100 year period, these statistics indicate that total land subsidence in the
range of 126 to 208 mm will occur over the Port Adelaide coastal area
(Belperio, 1993).
Subsidence monitoring data is also being used by Council in conjunction with
local sea level rise monitoring, to ascertain the potential risk of inundation that
may result from the coastal impacts of climate change in the future.
The
Port Adelaide and Lefevre Peninsula Seawater and Stormwater Study
(Stage 1)
2006
investigated the relationship between the existing land
subsidence trend in the area, and predicted sea level rise. The ongoing
subsidence needs to be considered in the investigations and planning for sea
level rise and related impacts in the area.
Acid sulphate soils
Also due in large part to the natural history of the area, the coastal area of the
City is prone to the development of acidic soils. Potential Acid Sulphate Soils
(PASS) are not a man-made contamination issue, but are naturally formed
when seawater, or sulphate-rich water, mixes with land or inter-tidal sediments
containing iron oxides and organic matter. When exposed to air due to drainage
or disturbance, these soils can produce sulphuric acid. ‘Potential acid sulphate
soils’ conditions are commonly associated with mangroves and protected low-
energy environments such as estuaries and coastal lakes.
Location
Average Subsidence (mm/yr)
Outer Harbour
1.42
Port Adelaide
1.26
Fort Glanville
2.08
EWS Depot (Ottoway)
1.54
